This invention relates to a process for the treatment of contact lenses and is particularly concerned with post-polymerization treatment of contact lenses in a method of manufacturing hydrated soft contact lenses.
It is known, after moulding contact lenses from a hydratable plastics material, to hydrate the lenses at an elevated temperature in a vessel containing a hydration fluid such as a 1% by wt. sodium bicarbonate solution. Following hydration, the contact lenses are removed from the vessel, washed and then introduced into individual receptacles or wells where they are immersed in saline solution; the wells are then closed and sealed with a foil cover so that the contact lenses are stored individually in packages in saline solution for distribution and sale. However, such a procedure causes problems in handling of the lenses during and after hydration. It is particularly difficult to handle contact lenses after hydration because they are relatively soft and prone to damage.
It is also known to hydrate contact lenses in the final packages in which they are sealed, distributed and sold. However, unwanted contaminants resulting from the polymerisation reaction leach out of the lenses into the surrounding fluid in which the lenses are packaged. This can cause irritation to the lens wearer. High levels of certain contaminants may not be permissible in some countries.
It is an object of the present invention to provide an improved method of treating contact lenses in a method of manufacturing hydrated soft contact lenses which permits the removal of unwanted contaminants from soft contact lenses during their manufacture.
According to a first aspect of the present invention there is provided a method of treating a contact lens disposed in a well containing hydration fluid, such that a concave surface of the lens faces upwardly and the lens is submerged in the hydration fluid, thereby allowing contaminants to leach out of the lens into the hydration fluid, comprising the steps of:
introducing, after hydration of the lens is complete, a washing fluid into the well and removing contaminated hydration fluid from the well so as to replace at least some of the contaminated hydration fluid in the well with the washing fluid in a predetermined fluid-exchange procedure,
wherein the washing fluid is introduced into the well so as to be directed against the concave surface of the lens and the contaminated hydration fluid is removed at a removal location remote from where the washing fluid impinges against the lens, such that the action of the introduced washing fluid serves to oppose movement of the lens towards the removal location.
Prior to introduction of the washing fluid, the method preferably includes the steps of:
(i) introducing the lens hydration fluid into the well directed against the upwardly facing concave surface of the lens so as to control the position of the lens within the well, until the lens is submerged; and
(ii) allowing sufficient time for the lens to hydrate and for contaminants to leach from the lens.
It will be appreciated that, during hydration, the lens swells and changes shape and it is important to maintain the lens submerged in the hydration fluid during this procedure without constraining it unduly. By directing the lens hydration fluid against the lens, the lens can be maintained in position within the well and prevented from floating on the hydration fluid as the well is filled.
Preferably, the washing fluid is introduced in at least two streams which are preferably mutually inclined so as to be directed against different regions of the lens. The washing fluid preferably has substantially the same chemical composition as the hydration fluid although the washing fluid may be at least partially constituted by lens storage fluid (e.g. saline).
Preferably, the contaminated hydration fluid is removed in at least two separate steps during which removal of the contaminated hydration fluid takes place at a greater rate than introduction of the washing fluid, the removal and introduction being timed so that sufficient fluid remains in the well to ensure that the lens remains submerged.
Contaminants may leach into the washing fluid in the well, thus the method may include a step of removing contaminated washing fluid and replacing it with fresh washing fluid which maybe at least partially constituted by lens storage fluid. Preferably, the contaminated washing fluid is removed and the fresh washing fluid is introduced in the same way as the removal and introduction of the contaminated hydration fluid and the washing fluid respectively.
Most preferably, the well in which the method of the present invention is performed is a well in which the contact lens is sealed and stored for distributed and sale, and the method further includes the step of sealing the well with the contact lens therein. The well may provided by a container of the type disclosed in our copending International Patent Application No. WO 99/06300.
In the mass production of soft contact lenses, it is important to ensure that the lenses have been properly treated and, in some countries, regulations require rejection of lenses which have not been subjected to the required treatment (e.g. insufficient removal of impurities from the lenses).
According to a second aspect of the present invention there is provided a method of treating a contact lens disposed in a well containing hydration fluid, such that a concave surface of the lens faces upwardly and the lens is submerged in the hydration fluid, thereby allowing contaminants to leach out of the lens into the hydration fluid, comprising the steps of:
introducing, after hydration of the lens is complete, a washing fluid into the well and removing contaminated hydration fluid from the well so as to replace at least some of the contaminated hydration fluid in the well with the washing fluid in a predetermined fluid-exchange procedure, and
monitoring the predetermined fluid-exchange procedure, whereby to establish whether the predetermined fluid-exchange procedure has ben correctly performed.
The method of said second aspect may be used in combination with the method of said first aspect.
Preferably, said monitoring step utilises first and second level sensors for sensing the level of fluid in the well, the first level sensor being arranged to signal when the level of the fluid is at a first, relatively higher, level and the second sensor being arranged to signal when the level of the fluid in the well is at a second, relatively lower, level. Thus, in a preferred embodiment, a predetermined volume of the lens hydration fluid is introduced into the well (the predetermined volume of hydration fluid being such that, when the well and sensors are correctly mutually presented, the sensor(s) signal that the level of fluid is at least at the relatively lower level and preferably at the relatively higher level); following which the hydration fluid is removed from the well whilst supplying the washing fluid into the well, the rate of removal of the hydration fluid being greater than the introduction rate of the washing fluid so that the fluid level reduces until the second sensor indicates that the level of fluid has reached the second (relatively lower) level; following which fluid removal is stopped and subsequently fluid introduction is also stopped when the first sensor indicates that the level of fluid is at the first (relatively higher) level; and the monitoring step includes checking that the sensors have signalled in the correct sequence and at the correct times having regard to the predetermined fluid-exchange procedure. If the predetermined procedure has not been validated, then the contact lens is rejected.
Preferably, the fluid removal during the fluid-exchange procedure is conducted in more than one discrete step. In a preferred embodiment, the level of the fluid in the well fluctuates around the lower level, the fluid removal being stopped and started under the control of the second sensor.
In an alternative embodiment, fluid removal is stopped when the second sensor indicates that the fluid has passed below the second level, and is started when the first sensor indicates that the fluid has reached the first level, so that the fluid fluctuates between the first and second levels.
It will be understood that the overall proportion of contaminated hydration fluid replaced by washing fluid in each exchange procedure is dependent upon the number of fluid removal steps performed, the rate and duration of washing fluid dosing and the efficiency of fluid mixing in the well.
As an alternative to introducing a predetermined volume of hydration fluid into the well, the hydration fluid may be introduced into the well until the first sensor indicates that the level of fluid is at the first (higher) level.
Preferably, the positioning of the second sensor is such as to ensure that the lens remains submerged throughout the fluid-exchange procedure.